Simian Immunodeficiency Virus (SIV) causes an AIDS-like disease in experimentally infected rhesus monkeys. SIV shares the morphology, CD4+ tropism, genome structure and serological cross-reactivity with the human immunodeficiency virus (HIV), the causative agent of Human Acquired Immunodeficiency Syndrome (AIDS). Therefore, SIV may be one of the best animal models for studying potential treatments for human AIDS. The long- term objective of this proposal is to design strategies by which engineered nucleic acids of defined sequence (antisense RNAs or antiviral genes) will prevent or cure infection by AIDS virus without killing the host cell. The specific aims are the following: 1. To deliver antisense sequences (or antiviral gene) into CD4+ lymphocytes and bone marrow cells resulting in resistance to viral infection. 2. To develop a CD4+ cells targeting system by which the antisense sequences or antiviral gene can be specifically targeted into Cd4+ cells (or the potential hosts for AIDS virus). 3. To evaluate the in vivo applicability of antisense approach using SCID mice model. To achieve these specific aims, the following methodologies will be taken. a) Antisense sequences complementary to varied regions of viral genes will be expressed by murine retroviral vectors. These retroviral vectors can be packaged by amphotropic helper cell line. The recombinant viruses synthesized by producer lines will be used to transduce CD4+ cells and bone marrow cells. Virus replication will be monitored in those transduced cells after infecting with wild type virus. b) Taking the advantage of CD4+ binding ability of SIV-envelope protein, we will use the structure genes of SIV to construct a CD4 tropism packaging helper line. The packaging signal of SIV will be incorporated into murine retroviral vector. c) A non-integrating viral vector will be developed by deleting some viral sequence which is involved in viral integration. This vector may increase the safety of using traditional retroviral vector. d) The in vivo applicability of this approach will be evaluated in bone marrow cell culture and SCID mice model. The bone marrow cells from donors will be transduced by antisense (or antiviral) recombinant viruses, then challenged with SIV or HIV. The viral activity of these bone marrow cells will be monitored in tissue culture as well as after injecting into SCID mice.